150 THE DESCENT OF MAN. Part I. 



surprising that man should differ so greatly in hairi- 

 ness from all his lower brethren, for characters gained 

 through sexual selection often differ in closely-related 

 forms to an extraordinary degree. 



According to a popular impression, the absence of a 

 tail is eminently distinctive of man ; but as those apes 

 which come nearest to man are destitute of this organ, 

 its disappearance does not especially concern us. Never- 

 theless it may be well to own that no explanation, as 

 far as I am aware, has ever been given of the loss of the 

 tail by certain apes and man. Its loss, however, is not 

 surprising, for it sometimes differs remarkably in length 

 in species of the same genera: thus in some species 

 of Macacus the tail is longer than the whole body, con- 

 sisting of twenty-four vertebrae ; in others it consists of a 

 scarcely visible stump, containing only three or four 

 vertebrae. In some kinds of baboons there are twenty- 

 five, whilst in the mandrill there are ten verv small 

 stunted caudal vertebrae, or, according to Cuvier, 79 some- 

 times only five. This great diversity in the structure and 

 length of the tail in animals belonging to the same genera, 

 and following nearly the same habits of life, renders it 

 probable that the tail is not of much importance to 

 them ; and if so, we might have expected that it would 

 sometimes have become more or less rudimentary, in 

 accordance with what we incessantly see with other struc- 

 tures. The tail almost always tapers towards the end 

 whether it be long or short; and this, I presume, re- 

 sults from the atrophy, through disuse, of the terminal 

 muscles together with their arteries and nerves, lead- 

 ing to the atrophy of the terminal bones. With respect 



79 Mr. St. George Mivart, ' Proc. Zoolog. Soc' 1865, p. 562, 583. 

 Dr. J. E. Gray, 'Cat. Brit. Mus. : Skeletons.' Owen, 'Anatomy of 

 Vertebrates,' vol. ii. p. 517. Isidore Geoffrov, 'Hist. Nat. Ge'n.' tom. 

 li p. 244. 



